Don't forget about state legislatures special elections, we are losing them this year
Republicans have flipped 4 seats from blue to red in special elections. Last year we flipped a net 8 seats from red to blue and in 2017 we flipped a net of 13. Don't let the Presidential primary distract you, from those special elections. They count too, and are part of the keeping the momentum going through 2020. If you have money or time, please check out to see where and when the next special elections are
From the link in the OP:
Showing two races March 12, another March 19.
They don't get the same attention, turnout is low, but every seat counts and pundits are paying attention. In 2018, they were taken as signs Democrats were fired up. We don't want to 2019 to be the year Democrats went back to sleep. Your time or money will be a lot more helpful in a legislative election right now than for the presidential primaries still almost a year away.